1. Field of the Invention
The present invention generally relates to universal serial bus (USB), and more particularly to a stream context cache system.
2. Description of Related Art
Universal Serial Bus (USB) is widely used in electronic devices for transferring data between a host and a peripheral device. The data transfer speed of USB 1.0 is 1.5 million bits per second (low speed) and 12 million bits per second (full speed). The data transfer speed of USB 2.0 is 480 million bits per second (high speed). USB 3.0 is released now and the data transfer speed of USB 3.0 is 4.8 billion bits per second (super speed). The detail description of USB 3.0 may be referred to “Universal Serial Bus 3.0 Specification.”
In a USB system, the data transfer between the host and the device is controlled by a host controller, and the communication between the host controller and the host is specified in a host controller interface (HCI), for example, “eXtensible Host Controller Interface for Universal Serial Bus (xHCI)”.
In the USB system specified by xHCI, the data structure of the transfer request block (TRB) is utilized in the data transfer. A TRB ring or a transfer ring consisted of a number of the TRBs is used for transferring data between the host and the USB device. In addition, the xHCI specifies a data structure of a data stream context, which provides a pointer for pointing to the TRB ring in the stream. In other words, the stream context must be transferred whenever the TRB is read.
Repetitive TRB readings occur in a conventional USB system. The details of the repetitive readings in the conventional USB system are discussed in an application entitled “Transfer Request Block Cache System and Method,” to the same assignee of the present application, the disclosure of which is hereby incorporated by reference.
For the reason that the host controller must read the stream context from the system memory whenever the data is transferred, this will cause time delay, time waste and power consumption, and thus reduce overall system efficiency. Therefore, a need has arisen to propose a novel scheme for decreasing read time, thereby increasing the system efficiency and lowing power consumption.